Java Timer.delay help

Technical Java
1

So we are trying to move away from Timer.Delay in our robot code because we are aware of the lag it brings to the whole robot when we are trying to reload the shooter. I am trying to find a way to implement a wait function with the Timer.getFPGATimestamp, but I’m drawing blanks on how to implement it.

I’m postulating that I’d have to implement by resetting the timer, then implementing something like this:

public boolean hasPeriodPassed(double period) {
if (timer.getFPGATimestamp() < period * 1000000) {
return true;
}
else {
return false;
}
}
}

But we got no results when we tried it like this.

An example of where we implement Timer.delay looks like this:

public void Fire() {
IntakeDown.set(false);
IntakeUp.set(true);
isIntakeUp = true;
Timer.delay(0.25);
shooterLatch.set(false);
shooterUnlatch.set(true);
Timer.delay(1.0);
isLatched = false;
isBottom = false;
isReset = false;
isFired = true;

}

If someone could point me in the right direction, it would be greatly appreciated.

2

You don’t need to multiply period. Timer.getFPGATimestamp() returns seconds; not milliseconds, microseconds or nanoseconds.

3

Yeah I figured that, but when I deleted that part. It still did not work correctly.

4

You need to save the current value of Timer.getFPGATimestamp() to compare it to, since it wont always be 0.

5

Here is an example of setting/tracking a start time as you transition through your fire sequence. It is broken out into one private attribute (time the sequence was started) and three helper methods.

NOTE: This assumes you are programming using the SimpleRobot framework.


    // This will be set to the time when the fire sequence was started. It
    // will be reset to 0 when the fire sequence completes

    private double fireSequenceStart = 0.0;

    /**
     * Helper method to indicate whether we are currently firing.
     */

    public boolean isFiring() {
        // When the fire start time is set to a non-zero value, then
        // we are firing
        return (fireSequenceStart != 0);
    }

    /**
     * Helper method to start the fire sequence (call this after a certain
     * button has been pressed during operatorControl(), or call it from
     * autonomous() if you want to fire then).
     */
    public void fire() {
        // Don't start a second fire sequence until the first completes
        if (isFiring() == false) {

            // Save time the fire sequence was started at
            fireSequenceStart = Timer.getFPGATimestamp();

            // Not sure if you want this, but you may want to clear your
            // internal "isFired" flag here if you don't clear it elsewhere
            // isFired = false;
        }
    }

    /**
     * Repeatedly call this method from your main loop in operatorControl() or
     * autonomous(). It should take you through your fire sequence without
     * blocking (requires no Timer.delay() calls).
     *
     * ***WARNING*** Make sure your other code does not block or have delays in
     * it, or this timing sequence may fail!
     */

    public void updateFireState() {
        if (isFiring() == true) {
            // Determine number of seconds into fire sequence
            double secsElapsed = Timer.getFPGATimestamp() - fireSequenceStart;

            // This is an attempt to refactor your original Fire() code
            // to change states based on the time elapsed (but with no Timer.delay() calls)
            if (secsElapsed < 0.25) {
                // State for first quarter second (0.0 to 0.25)
                IntakeDown.set(false);
                IntakeUp.set(true);
                isIntakeUp = true;
            } else if (secsElapsed < 1.25) {
                // State for the next second (0.25 to 1.0)
                shooterLatch.set(false);
                shooterUnlatch.set(true);
                // Hmmm, shouldn't isIntakeUp be set to false here?
            } else {
                // Finished (1.25 seconds have elapsed)

                // Reset start time to 0 (indicates we are done with the fire sequence)
                fireSequenceStart = 0;
                isLatched = false;
                isBottom = false;
                isReset = false;
                isFired = true;
            }
        }
    }

Hope that helps.

6

We use edu.wpi.first.wpilibj.Timer liberally. See our Catapult subsystem code:

7